"It is the same coenzyme Q that is marketed as a health supplement and used in cosmetics," says Dunlap.

Chemical contamination of fish can be hard to pick up unless it actually kills the fish.

In order to pick up low-level contamination, that can cause sub-lethal effects, scientists look to bio-indicators - biochemical markers in the animal that indicate something is wrong.

For the past 25 years, scientists have been using detoxification enzymes called mixed function oxidases as bio-indicators. These enzymes, which oxidise contaminants, increase in number when there are pollutants around.

This method can be unreliable because enzymes can be changed by factors other than the level of pollutants, says Dunlap.

"Enzyme can be denatured depending on how you handle them, which will affect the assay," says Dunlap. "And it could compromise the test."

Different measurements

Dunlap and colleagues have developed a test that measures a different biological process involving Coenzyme Q.

This chemical, involved in transporting electrons during aerobic respiration and has two forms: an oxidised form and a reduced form.

The reduced form is a powerful antioxidant, which protects against oxidative stress caused by pollutants.

When a pollutant is present, an enzyme is activated that converts the oxidised form to the reduced form, measurably changing what is called the Coenzyme Q redox balance.

Because the test measures the products of a detoxification enzyme's activity, rather than the enzyme directly, it is not vulnerable to extra factors that can affect enzyme levels, says Dunlap.

He says the Coenzyme Q redox balance is also used to measure oxidative stress in humans.

Changing the ratio

Dunlap and colleagues' new test involves extracting a sample from the liver of a test fish, and measuring the ratio of the reduced to oxidised form of Coenzyme Q.

"You get an increase in the reduced form [when pollutants are present]," says Dunlap.

Dunlap says because the test relies on measuring a ratio, the results are less vulnerable to being skewed by laboratory procedures that might change the absolute amounts of the different forms of Coenzyme Q.

Dunlap and colleagues tested the effectiveness of the new test in the laboratory by injecting barramundi with different amounts of polycyclic aromatic hydrocarbons (PAHs), a common pollutant from such things as fuel spills and urban run-off.

They then checked to see if the test picked up the correct levels of contaminant injected into the fish.

Lab experiments found the new test was just as effective and faster than a mixed function oxidase-based test, but this still needs to confirmed in the field, says Dunlap.

The researchers are now looking to see if the test can be used to check for heavy metal contamination.